The collets of machines which operate at high rotational speeds, such as drilling machines and routers used in the production of printed circuit boards, long have caused problems of considerable significance. One has involved the necessity for achieving balance of the rotating components of the spindle. Conventional spindles incorporate strong springs for holding the collets in their closed positions. These springs must flex as the collet is moved from the opened to the closed position, causing them to change their positions and, hence, destroying rotational balance. Even a small amount of imbalance in machines that rotate at high speeds will greatly reduce bearing life. Frequent expensive overhauls become necessary.
Moreover, a conventional collet will grip the shank of the tool bit only at a single plane. This results because of inevitable manufacturing tolerances. Tapers and diameters rarely if ever can be matched exactly so that the gripping force necessarily is localized at some circumferential portion of the tool shank, rather than extending along the length of the collet. Side pressure on the tool, such as encountered by a router bit, is reversed with each revolution. As a result, the tool rocks slightly as it rotates. Gradually, it can creep out of the collet. This condition exists despite the customary application of an augmented holding force on the collet of a router.